/*
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program. If not, see <http://www.gnu.org/licenses/>.
 */
package org.merak.core.model;

public abstract class SingletonHolder {

	//~ Attributes ///////////////////////////////////////////////////////////////
	//****************************************************************************
	private Object   instance    = null;
	private boolean  instancing  = false;

	//~ Methods //////////////////////////////////////////////////////////////////
	//****************************************************************************
	public abstract Object newInstance();

	//****************************************************************************
	public synchronized void deleteInstance() {
		this.instance = null;
	}

	//****************************************************************************
	public synchronized Object getInstance()	{

		if (this.instance == null) try {
			// Check for Singleton Lock
			if (this.instancing) throw new InstantiationException (
					"Singleton DeadLock detected: " +
					"getInstance() called recursively"
			);
			// Create a new instance
			this.instancing = true;
			this.instance   = this.newInstance();
		}
		catch (Exception e) {
			throw new Error("Error during Singleton instantiation",e);
		}
		finally {
			/* Make sure you set singleton instancing to false,
			 * as it might alert false dead locks */
			this.instancing = false;
		}
		return this.instance;

	}
	//****************************************************************************

}
